I am learning node.js
for example, I try
var server = require("./myserver.js");
and
var server = require("./myserver");
why do both work? What is this kind of things call?
If you take a look at node's source code for the require-function, you can see that require's load-function calls a function findLongestRegisteredExtension to determine the file-extension. This function returns .js as its default value if no extension could be determined:
function findLongestRegisteredExtension(filename) {
const name = path.basename(filename);
let currentExtension;
let index;
let startIndex = 0;
while ((index = name.indexOf('.', startIndex)) !== -1) {
startIndex = index + 1;
if (index === 0) continue; // Skip dotfiles like .gitignore
currentExtension = name.slice(index);
if (Module._extensions[currentExtension]) return currentExtension;
}
return '.js';
}
That's why using both require("./myserver.js"); or require("./myserver"); will resolve the same module.
Related
I have a function to make capitalize every first word in nodejs expressjs like this:
function titleCase(str) {
var splitStr = str.toLowerCase().split(' ');
for (var i = 0; i < splitStr.length; i++) {
// You do not need to check if i is larger than splitStr length, as your for does that for you
// Assign it back to the array
splitStr[i] = splitStr[i].charAt(0).toUpperCase() + splitStr[i].substring(1);
}
// Directly return the joined string
return splitStr.join(' ');
}
But how can i use that function in global? So i can use that in my controller.
I have tried to make function.js file:
module.exports = {
titleCase: function(str) {
var splitStr = str.toLowerCase().split(' ');
for (var i = 0; i < splitStr.length; i++) {
// You do not need to check if i is larger than splitStr length, as your for does that for you
// Assign it back to the array
splitStr[i] = splitStr[i].charAt(0).toUpperCase() + splitStr[i].substring(1);
}
// Directly return the joined string
return splitStr.join(' ');
}
}
and require function.js file in server.js like this:
require('./app/helpers/function');
But its still not working.
There are several ways to do this, just make sure the syntax is right.
If you don't know the difference between these two things below or when to use them, you should read about it.
Simplest way:
exports.titleCase = function(str) {
// function here
}
Module.exports way:
function titleCase(str) {
// function here
}
module.export = {
titleCase,
}
And require for both:
// Require
const {titleCase} = require('./app/helpers/function');
// => titleCase("something");
// or
const func = require('./app/helpers/function');
// => func.titleCase("something")
global['titleCase'] = require('./app/helpers/function');
please update your server.js with global['titleCase'] = require('./app/helpers/function'); instead of require('./app/helpers/function');
I am trying to initialize a key class in a node.js program, but the instructions are running in arbitrary order and therefore it is initializing wrong. I've tried both making initialization happen in the definition and in a separate function; neither works. Is there something that I'm missing?
Current code:
class BotState {
constructor() {
this.bios = {}
this.aliases = {};
this.stories = {};
this.nextchar = 0;
}
}
var ProgramState = new BotState();
BotState.prototype.Initialize = function() {
this.bios = {};
var aliases = {};
var nextchar = 0;
this.nextchar = 0;
fs.readdir(biosdir, function (err, files) {
if (err) throw err;
for (var file in files) {
fs.readFile(biosdir + file + ".json", {flag: 'r'}, (err, data) => {
if (err) throw err;
var bio = JSON.parse(data);
var index = bio["charid"];
this.bios[index] = bio;
for (var alias in bio["aliaslist"]) {
this.aliases[bio["aliaslist"][alias].toLowerCase()] = index;
}
if (index >= nextchar) {
nextchar = index + 1;
}
})
}
this.stories = {};
this.nextchar = Math.max(Object.keys(aliases).map(key => aliases[key]))+1;
});
}
ProgramState.Initialize();
Is there some general way to make node.js just... run commands in the order they're written, as opposed to some arbitrary one?
(Apologies if the code is sloppy; I was more concerned with making it do the right thing than making it look nice.)
You are running an asynchronous operation in a loop which causes the loop to continue running and the asynchronous operations finish in some random order so you process them in some random order. The simplest way to control your loop is to switch to the promise-based version of the fs library and then use async/await to cause your for loop to pause and wait for the asynchronous operation to complete. You can do that like this:
const fsp = require('fs').promises;
class BotState {
constructor() {
this.bios = {}
this.aliases = {};
this.stories = {};
this.nextchar = 0;
}
}
var ProgramState = new BotState();
BotState.prototype.Initialize = async function() {
this.bios = {};
this.nextchar = 0;
let aliases = {};
let nextchar = 0;
const files = await fsp.readdir(biosdir);
for (const file of files) {
const data = await fsp.readFile(biosdir + file + ".json", {flag: 'r'});
const bio = JSON.parse(data);
const index = bio.charid;
const list = bio.aliaslist;
this.bios[index] = bio;
for (const alias of list) {
this.aliases[alias.toLowerCase()] = index;
}
if (index >= nextchar) {
nextchar = index + 1;
}
}
this.stories = {};
// there is something wrong with this line of code because you NEVER
// put any data in the variable aliases
this.nextchar = Math.max(Object.keys(aliases).map(key => aliases[key]))+1;
}
ProgramState.Initialize();
Note, there's a problem with your usage of the aliases local variable because you never put anything in that data structure, yet you're trying to use it in the last line of the function. I don't know what you're trying to accomplish there so you will have to fix that.
Also, note that you should never use for/in to iterate an array. That iterates properties of an object which can include more than just the array elements. for/of is made precisely for iterating an iterable like an array and it also saves the array dereference too as it gets you each value, not each index.
I've tested some buffer swap function in NodeJS, but in my Meteor project it doesn't work.
Can somebody tell me the reason?
Nodejs:
var CRC = new Buffer([0x20,0x40]);
console.log(CRC.swap16()); // OUTPUT: <Buffer 40 20>
Meteor.js
var CRC = new Buffer([0x20,0x40]);
console.log(CRC.swap16()); // OUTPUT: TypeError: CRC.swap16 is not a function
Can somebody help me please. In know it's maybe a version problem. but i can't solve it at the moment.
Is there also a way to get this thing running with meteor?
Buffer.swap16() method has been added in 5.10.0, whereas Meteor uses NodeJS version 4.
You can copy this method implementation from the NodeJS source, it is quite simple (with small modifications):
function swap(b, n, m) {
const i = b[n];
b[n] = b[m];
b[m] = i;
}
Buffer.prototype.swap16 = function swap16() {
const len = this.length;
if (len % 2 !== 0) {
throw new RangeError('ERR_INVALID_BUFFER_SIZE', '16-bits');
}
for (var i = 0; i < len; i += 2) {
swap(this, i, i + 1);
}
return this;
};
EDIT: I'm using node v8.0.0
I just started learning how to access SQL databases with node-postgres, and I'm having a little bit of trouble accessing multiple databases to collect the data in a work able format, particularly with executing multiple queries within forEach loops. After a few tries, I'm trying async/await, but I get the following error:
await client.connect()
^^^^^^
SyntaxError: Unexpected identifier
When I tried using a pool or calling .query sequentially, I would get something along the lines of
1
[]
could not connect to postgres Error: Connection terminated
Here is an abbreviated version of my code:
const { Client } = require('pg');
const moment = require('moment');
const _ = require('lodash');
const turf = require('#turf/turf');
const connString = // connection string
var collected = []
const CID = 300
const snaptimes = // array of times
var counter=0;
const client = new Client(connString);
function createArray(i,j) {
// return array of i arrays of length j
}
await client.connect()
snaptimes.forEach(function(snaptime){
var info = {}; // an object of objects
// get information at given snaptime from database 1
const query1 = // parametrized query selecting two columns from database 1
const result1 = await client.query(query1, [CID,snaptime]);
var x = result1.rows;
for (var i = 0; i < x.length; i++) {
// store data from database 1 into info
// each row is an object with two fields
}
// line up subjects on the hole
const query2 = // parametrized query grabbing JSON string from database 2
const result2 = await client.query(query2, [CID,snaptime]);
const raw = result2.rows[0].JSON_col;
const line = createArray(19,0); // an array of 19 empty arrays
for (var i = 0; i < raw.length; i++) {
// parse JSON object and record data into line
}
// begin to collect data
var n = 0;
var g = 0;
// walk down the line
for (var i = 18; i > 0; i--) {
// if no subjects are found at spot i, do nothing, except maybe update g
if ((line[i] === undefined || line[i].length == 0) && g == 0){
g = i;
} else if (line[i] !== undefined && line[i].length != 0) {
// collect data for each subject if subjects are found
line[i].forEach(function(subject){
const query 3 = // parametrized query grabbing data for each subject
const result3 = await client.query(query3,[CID,subject,snaptime]);
x = result3.rows;
const y = moment(x[0].end_time).diff(moment(snaptime),'minutes');
var yhat = 0;
// the summation over info depends on g
if (g===0){
for (var j = i; j <= 18; j++){
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
} else {
for (var j = i; j <= 18; j++){
if (i<j && j<g+1) {
yhat = moment.duration(info[j].field2).add(yhat,'m').asMinutes();
} else {
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
}
}
collected.push([y,yhat,n,i]);
});
}
n+=line[i].length;
g=0;
}
// really rough work-around I once used for printing results after a forEach of queries
counter++;
if (counter===snaptimes.length){
console.log(counter);
console.log(collected);
client.end();
}
});
The problem is caused by your forEach callback not being async:
snaptimes.forEach(function(snaptime){
should be:
snaptimes.forEach(async function (snaptime) {
for the await to be recognizable at all.
Keep in mind that an async function returns immediately and it returns a promise that gets eventually resolved by return statements of the async function (or rejected with uncaught exceptions raised inside the async function).
But also make sure your Node version supports async/await:
Since Node 7.6 it can be used with no --harmony flag.
In Node 7.x before 7.6 you have to use the --harmony flag.
It was not available in Node before 7.0.
See: http://node.green/#ES2017-features-async-functions
Also note that you can use await only inside of functions declared with the async keyword. If you want to use it in the top level of your script or module then you need to wrap it in an immediately invoked function expression:
// cannot use await here
(async () => {
// can use await here
})();
// cannot use await here
Example:
const f = () => new Promise(r => setTimeout(() => r('x'), 500));
let x = await f();
console.log(x);
prints:
$ node t1.js
/home/rsp/node/test/prom-async/t1.js:3
let x = await f();
^
SyntaxError: Unexpected identifier
but this:
const f = () => new Promise(r => setTimeout(() => r('x'), 500));
(async () => {
let x = await f();
console.log(x);
})();
prints:
$ node t2.js
x
after 0.5s delay, as expected.
On versions of Node that don't support async/await the first (incorrect) example will print:
$ ~/opt/node-v6.7.0/bin/node t1.js
/home/rsp/node/test/prom-async/t1.js:3
let x = await f();
^
SyntaxError: Unexpected identifier
and the second (correct) example will print a different error:
$ ~/opt/node-v6.7.0/bin/node t2.js
/home/rsp/node/test/prom-async/t2.js:3
(async () => {
^
SyntaxError: Unexpected token (
It's useful to know because Node versions that don't support async/await will not give you a meaningful error like "async/await not supported" or something like that, unfortunately.
Make sure that you should use async block outside like:
async function() {
return await Promise.resolve('')
}
And it is default supported after node 7.6.0. Before 7.6.0, you should use --harmony option to work for it.
node -v first to check your version.
First of all, you don't know enough about async-await just yet. don't worry, it's actually quite easy; but you need to read the documentation to be able to use that stuff.
More to the point, the problem with your code is that you can only await inside async functions; you're doing that outside of any function.
First of all, here's the solution that is closest to the code you wrote:
const { Client } = require('pg');
const moment = require('moment');
const _ = require('lodash');
const turf = require('#turf/turf');
const connString = // connection string
var collected = []
const CID = 300
const snaptimes = // array of times
var counter=0;
const client = new Client(connString);
function createArray(i,j) {
// return array of i arrays of length j
}
async function processSnaptime (snaptime) {
var info = {}; // an object of objects
// get information at given snaptime from database 1
const query1 = // parametrized query selecting two columns from database 1
const result1 = await client.query(query1, [CID,snaptime]);
var x = result1.rows;
for (var i = 0; i < x.length; i++) {
// store data from database 1 into info
// each row is an object with two fields
}
// line up subjects on the hole
const query2 = // parametrized query grabbing JSON string from database 2
const result2 = await client.query(query2, [CID,snaptime]);
const raw = result2.rows[0].JSON_col;
const line = createArray(19,0); // an array of 19 empty arrays
for (var i = 0; i < raw.length; i++) {
// parse JSON object and record data into line
}
// begin to collect data
var n = 0;
var g = 0;
// walk down the line
for (var i = 18; i > 0; i--) {
// if no subjects are found at spot i, do nothing, except maybe update g
if ((line[i] === undefined || line[i].length == 0) && g == 0){
g = i;
} else if (line[i] !== undefined && line[i].length != 0) {
// collect data for each subject if subjects are found
line[i].forEach(function(subject){
const query 3 = // parametrized query grabbing data for each subject
const result3 = await client.query(query3,[CID,subject,snaptime]);
x = result3.rows;
const y = moment(x[0].end_time).diff(moment(snaptime),'minutes');
var yhat = 0;
// the summation over info depends on g
if (g===0){
for (var j = i; j <= 18; j++){
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
} else {
for (var j = i; j <= 18; j++){
if (i<j && j<g+1) {
yhat = moment.duration(info[j].field2).add(yhat,'m').asMinutes();
} else {
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
}
}
collected.push([y,yhat,n,i]);
});
}
n+=line[i].length;
g=0;
}
// really rough work-around I once used for printing results after a forEach of queries
counter++;
if (counter===snaptimes.length){
console.log(counter);
console.log(collected);
}
}
async function run () {
for (let snaptime of snaptimes) {
await processSnaptime(snaptime);
}
}
/* to run all of them concurrently:
function run () {
let procs = [];
for (let snaptime of snaptimes) {
procs.push(processSnaptime(snaptime));
}
return Promise.all(procs);
}
*/
client.connect().then(run).then(() => client.end());
client.connect returns a promise and I use then to call run once it's resolved. When that part is over, client.end() can be called safely.
run is an async function, therefore it can use await to make the code more readable. The same goes for processSnaptime.
Of course I can't actually run your code, so I can only hope I didn't make any mistakes.
I am working on creating a static node.js server that just serves up the plain html, css, and javascript that is in the specified directory. I am trying to get the server to read every subdirectory and route the url to the file it specifies. However it only reads the root directory.
var fs = require('fs');
var array = fs.readdirSync(__dirname);
function getAllSub(array){
for (i = 0; i < array.length; i++){
if (array[i].indexOf(".") == (-1))
{
array = array.concat(array[i] + "/" + fs.readdirSync(__dirname + "/" + array[i]));
}
if (array[i].indexOf("/") != (-1)){
var foldcon = array[i].substr(array[i].indexOf("/") + 1);
var folder = array[i].substr(0, array[i].indexOf("/"));
foldcon = foldcon.split(",");
for (n = 0; n < foldcon.length; n++){
foldcon[n] = folder + "/" + foldcon[n]
if (foldcon[n].indexOf(".") == (-1)){
console.log([foldcon[n]]);
foldcon[n] = getAllSub([foldcon[n]]);
}
}
array.splice(i, 1, foldcon);
}
}
return array;
}
array = getAllSub(array);
console.log(array);
Right now this code reads the directory and it recognizes if an item in the array of files is a folder, however it doesn't add the files from the subdirectories into the array properly. Right now it kinda goes all infinite recursion, and I can't really figure out how to stop it.
This isn't meant to be something I am actually going to use, I just thought it would be a good project to work on to introduce myself to the basics of node.js
edited^
I know it's late, but this is the right answer for a recursive solution to reading file paths in sub-folders:
var fs = require("fs");
/**
* Recurse through a directory and populate an array with all the file paths beneath
* #param {string} path The path to start searching
* #param {array} allFiles Modified to contain all the file paths
*/
function readdirSyncRecursive(path, allFiles) {
var stats = fs.statSync(path);
if (stats.isFile()) {
// base case
allFiles.push(path);
} else if (stats.isDirectory()) {
// induction step
fs.readdirSync(path).forEach(function(fileName) {
readdirSyncRecursive(path + "/" + fileName, allFiles);
});
}
}
var allFiles = [];
readdirSyncRecursive("/path/to/search", allFiles);
console.info(allFiles);
var fs = require('fs');
var array = fs.readdirSync(__dirname);
for (i = 0; i < array.length; i++){
if (array[i].indexOf(".") == (-1))
{
// you need to use the return value from concat
array = array.concat(array[i] + "/" + fs.readdirSync(__dirname + "/" + array[i]));
console.log('if executed');
}
}
console.log(array);